text:
How to interpret the term "standard" which is found in FAA's Obstacle Departure Procedures (ODP) and Standard Instrument Departure Procedures (SID)?
This might be obvious, but I find it difficult to interpret correctly the term "standard", when it refers to the takeoff phase of the flight.
Take, for example, the takeoff minimums for the La Guardia airport, page L16. For Runway 13, it states 400' ceiling height and 2¼ statute (I think) miles visibility but it does not mention any climb gradient. Is it implied that it follows the "standard" climb gradient of 200 feet per nautical mile? Next, it states that alternatively one can takeoff with the "standard" visibility rules, but only with a climb gradient of at least 280 FPNM until it reaches to 500 feet altitude. Which exactly are these standard visibility rules? The only source I remember finding states a requirement for 1 statute mile visibility for 1-2 engines aircrafts and 1/2 statute mile visibility for aircrafts with more than two engines, but no requirement for ceiling height.
Another example can be found by looking at this SID. Its takeoff minimums description states that for runway 4 "Standard" takeoff minimums apply. In addition, for runway 13, it states "400-2 or Standard with minimum climb of 280' per NM to 500." Does this mean that for "400 feet ceiling height - 2 statute miles visibility" the "standard" 200' per NM climb gradient applies, while for "standard" visibility a 280' per NM climb gradient is required?
I would be really grateful if someone could help me clarify the above rules.

The definition of standard minimum visibility for departure is found in CFR §91.175 Takeoff and landing under IFR.

f) Civil airport takeoff minimums. This paragraph applies to persons
operating an aircraft under part 121, 125, 129, or 135 of this
chapter.
(1) Unless otherwise authorized by the FAA, no pilot may takeoff from
a civil airport under IFR unless the weather conditions at time of
takeoff are at or above the weather minimums for IFR takeoff
prescribed for that airport under part 97 of this chapter.
(2) If takeoff weather minimums are not prescribed under part 97 of
this chapter for a particular airport, the following weather minimums
apply to takeoffs under IFR:
(i) For aircraft, other than helicopters, having two engines or less—1
statute mile visibility.
(ii) For aircraft having more than two engines— 1⁄2 statute mile
visibility.
(iii) For helicopters— 1⁄2 statute mile visibility.

The AIM 5−2−8 confirms your intuition about climb gradients.

b. What criteria is used to provide obstruction clearance during
departure?

Unless specified otherwise, required obstacle clearance for all departures, including diverse, is based on the pilot crossing the
departure end of the runway at least 35 feet above the departure end
of runway elevation, climbing to 400 feet above the departure end of
runway elevation before making the initial turn, and maintaining a
minimum climb gradient of 200 feet per nautical mile (FPNM), unless
required to level off by a crossing restriction, until the minimum IFR
altitude. A greater climb gradient may be specified in the DP to clear
obstacles or to achieve an ATC crossing restriction.

Note that visibility minimums do not apply to Part 91 aircraft. Also note that standard takeoff minimums do not have a minimum ceiling while published departure procedures almost always have a minimum ceiling or climb gradient—and often have both.

Thank you very much, that is exactly what I was looking for. Nevertheless, why does initial climb gradient depend on visibility, since obstacles around the airport have "fixed" heights?

The climb gradient applies until you have reached a specified altitude. They want to make sure that you can either see the obstacles or are climbing fast enough to miss them. Details are found in the TERPS. https://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentid/1032731


text:
If I have two 61.87(n)/(p) student solo endorsements, can I pick which one to operate under?
The backstory:
I am working on my US PPL. I started my training with Mr. D, and got most of what I needed for my solo with him except perfecting my landings. Mr. D felt he was having trouble helping me get my landings down, so he handed my off to Mr. J. I worked on landings with Mr. J and he felt I was ready to solo. We planned a day, but a day before, Mr. J had a family emergency that had him out of town for 2 weeks, so he handed my solo off to Mr. D.
Mr. D and I flew and he felt I was ready, so he signed me off for a 61.87(c) endorsement and I did a solo flight. We took a break (lunch) and then he signed me off for a 61.87(n) endorsement and I did another supervised solo.
On that second solo flight, the last landing was a flatish bounce that I think rattled me (figuratively & mentally) a bit. I ended up going around 3 times, but did land it successfully on that 3rd try. The next day the plane went into annual, which took 3 weeks.
So while I legally could go fly solo at that point, I then spent the next month training more landings with Mr. J. I now feel much more ready personally and have a feel for when to add power and what that will do while landing. Mr. J says he wants to do a solo flight in the next week, signing off a 61.87(p) endorsement as part of that.
The 61.87(n) endorsement Mr. D gave me still has a month and a half left. It states a limitation of 5 miles or greater visibility, no more than 8 knots direct crosswind. Mr. J has stated that his endorsement will come with a limitation of "written permission the day of the flight" - I will have to text and get permission before each flight.
One of the challenges of my flight training has been my work schedule not always been predictable, and one of the things I have been looking forward to with a solo endorsement is more flexibility schedule wise. I have nothing against asking a CFI for advice regarding a go/no go decision on a particular day, but if they are not available (camping as it usually is with Mr. J) I would like to be able to fly on days where the weather is clearly good. My general thought is if I have a hole open up in my (and the club plane's) schedule, I would text Mr. J, do a weather brief, go preflight the plane, and if I hadn't heard back, decide on my own, with an extra margin of "no go" bias for safety.
The question(s):
If I have two 61.87(n)/(p) student solo endorsements for overlapping time periods, can I pick which one to operate under or am I only allowed to operate by the most recent one? If I am only allowed to operate under the most recent, would I be unwise or unsafe to request to use my current endorsement until it expires? Does Mr. J have to be the one to have signed the most recent 61.87(n)/(p) endorsement to endorse further things, like cross country flights?

This is just a grown up version of "mom said no, but dad said yes." You really ought to be addressing this topic with your instructors. Regardless of any legal answer, maintaining a positive working relationship with each should guide your actions in this matter. That can only come from you getting them both on the same page WRT your training progress and solo privileges. Nothing good can come from playing one against the other.

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text:
How do you avoid power of 10 or order of magnitude errors when using an E6B calculator?
I am currently working through Gleim's instructions for using their E6B calculator.
It says: "The numbers on the inner and outer scales represent multiple sof 10 of the values shown." And "EXAMPLE: The number "20" on either scale me represent 0.2, 2.0, 20, 200, or 2,000".
I've been working through the examples, and a recurring problem is getting the right value to multiply by 10, but not knowing what power of 10 to multiply it by. (To put it in math terms: right mantissa, wrong exponent).
What is the process or rules to make sure you get the right answer every time? Obviously, getting a flight calculation wrong by an order of magnitude is not a problem you want to have!

It's not a problem you'll ever have in practice, as it will always be obvious to you whether that "2" on your wizz wheel is 0.2, 2, 20 or 200. It is not a problem you'll have with time/endurance etc issues as the inner scale of time is unmistakable.
But lets take some practical examples:
Conversion Nautical to statute miles

Set 90 next to the "NAUT" marking
Read the value next to the "STAT" marking. it is somewhere about 10.5.
You know that nautical miles and statute miles are fairly similar
You therefore know this cannot be 10 Statute miles, nor 0.1 so must be around 100
The answer is 103.5

Calculate speed from distance and time

Distance is 26NM and time is 13 minutes
Set 13 on the inner scale opposite 26 on the outer scale
The rate arrow points at the speed. It says 12.
I'm flying a standard single engine prop. Can it fly at 12 Knots? Can it fly at 1200 Knots?
The answer can only possibly be 120Knots

Fuel burn rate

You took 32 gallons of fuel and flew 4 hours 20 minutes
Set 4:20 on the inner time scale against 32 on the outer scale
Rate arrow points at 74.
Did I burn 74 Gallons per hour? My Cessna only holds 40! Did I burn 0.74? That seems awfully low - with that my endurance would be measured in days when I know its roughly 4 hours.
The answer can clearly only ever be 7.2 Gals/hour burn rate

The thing with being out by a factor of 10, is that it is always obvious you're out by a factor of 10. 2x, 3x even 4x you might get confused. But I don't think you ever will with 10x
The even shorter answer is that once you've gained your PPL you'll only ever pull out your E6B to answer these such questions, and any other time you'll use modern, electronic tools to answer these questions. Slide rules; gone from the classroom in the 1970's but still used to teach people to fly.

In other words: "Common sense". +1

@JörgWMittag yes, but this was the nicer way of saying that!

Plus mentally doing a round-off approximation gives you the rough answer including the order of magnitude. The E6B or slide rule just gives you a few digits more accuracy. For your examples, NM is close to SM so 90NM is close to 90SM - or, in this case, 103.5SM. 25 miles in 1/4 hour is about 25*4 or 100 MPH. 32 gallons in a little over 4 hours is a little less than 32/4 or 8 GPH.

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text:
How much difference in heading/bearing between consecutive legs is "officially" considered a turn?
While examining FAA's TERPS manual (Order 8260.3D) and PBN manual (Order 8260.58A), I noticed two seemingly contradictory statements.

TERPS 8260.3D Chapter 14. Departure Routes, 14-3-4 . Construct turning segments when the course change is more than 15 degrees

(emphasis mine)
Whereas in PBN manual, it seems that a deviation of 10 degrees is considered a turn.

PBN 8260.58A 1-2-5,b,(1)a . [...] Not applicable for FB turns of 10 degrees or less.

(emphasis mine)
Am I missing something. Is there any consistent rule that states when a transition between legs of an Instrument Procedure is considered a turn or a straight flight?

I believe the question might need to be restated.  Whether a change in heading is "considered a turn" or not isn't really the issue.  The documents you reference provide guidance for constructing a flyable procedure.  If a turn was an acute angle the question of fly-over vs lead turn, as well as turn radius, play a very large part in the path the aircraft takes over the ground, and hence dramatically affect the design of the procedure.  At angles less than 10 degrees it matters little whether you lead the turn or fly over it before changing heading.

More specifically, PBN 8260.58A 1-2-5,b,(1)a describes how to calculate DTA, (Distance Turn Anticipation).  It is not saying that turns less than 10 degrees are not officially considered turns, only that calculating the DTA is not applicable or necessary.

@MichaelHall thanks I really appreciate your input.

I will have to answer my own question, since I have noticed that in FAA's PBN Manual it states:

PBN 8260.58A 1-2-5c . Turn parameters. For OEA construction, a turn is indicated when the course change exceeds the alignment tolerance of 0.03 degrees.

So, at least as far as route design is concerned, the alignment threshold for turn indication is 0.03 degrees.


text:
Does TRACON airspace override Class B airspace in terms of control authority when controlling approach or departure procedures?
This is a simple schematic description of Class Airspace.
My understanding is that Class B has strict rules, specific lower and upper altitude limits and requires clearance to enter. However, I have also come across the Standard Operating Procedures Manual for the N90 TRACON (ORDER 7110.1D), which designate the sectors of local airspace differently. Those also define lower and upper altitude limits. Clearly, the N90 TRACON overlaps with the Class B airspace around the JFK, LGA, TEB and EWR airports.
My confusion has to do primarily with this overlap. I was thinking that Class B airspace has to do strictly with terminal procedures (approaches/departures), that is, all take-off and landing procedures take place within this airspace.
However, I have seen SID and STAR procedures running over fixes located close to the airports, which define much higher altitudes than the Class B upper limits (around JFK and the above airports, the upper limit is 7000ft for Class B airspace, while lower limits vary).
Take, for example, the LENDY SIX ARRIVAL, of JFK airport. I read over the JENNO fix information: "Expect FL230".
What is this supposed to mean: "Expect FL230"? Will an approaching aircraft enter the procedure at a Flight Level of 23000ft or be at that flight level whenever approaching the airport at that fix point? How does Class B relate to these operations? I thought that approach operations take place within Class B but I am confused because the altitudes I see in SID/STAR procedures or the lower/upper altitude limits in the various airspace sectors of Standard Operating Procedure (SOP) plans* are quite different. It appears as if flights that approach for arrival, for example, are controlled before entering Class B (i.e. at higher altitudes) when inside a TRACON, e.g. N90.
*(I cannot link to an SOP Manual because they are intended for internal distribution, so I cannot find something official online, however, the information is pretty much like that document).

Class B is a legal restriction for pilots. ATC has to give them clearance to enter it. It's there to protect the traffic around a busy airport from aircraft that are not being controlled by ATC.
The TRACON airspace is just for controllers. Pilots aren't expected to know sector boundaries. They don't have to worry about that at all. Each controller will tell the pilot the frequency to contact the next controller whose airspace they are about to enter. Few TRACONs make their sector boundaries public and they change often.
A pilot flying under VFR does not necessarily even need to talk to controllers outside of A, B, C or D airspace, regardless of what ATC sector he might be in.
As long as you have the correct type of transponder, it is entirely legal to fly VFR through the layer of air above the class B below 18,000 feet without contacting atc. (This is class E airspace). Whatever controller whose sector you're flying through will keep any IFR traffic away from you, but they don't need to give you vectors or anything. You have to stay away from clouds. It's entirely the pilot's responsibility to see and avoid things.*
SIDs and STARs are only used by IFR traffic that is being controlled by ATC, but not necessarily by TRACON the whole time. Some STARs start hundreds of miles from the airport. When they begin the arrival they will be controlled by en-route controllers, who will tell them when they need to switch to TRACON and what frequency to use.

* I'm leaving out flight following for simplicity.

I may not understand your question correctly but I think you are a little confused about Airspace here.  There is no TRACON airspace.  TRACON is defined here:
 https://en.wikipedia.org/wiki/Air_traffic_control#Approach_and_terminal_control
A TRACON is an ATC facility usually associated with Class B airspace.  Because the Class B airspace is so busy they usually have their own radar controllers instead of calling the tower directly or using ATC Center.  The documents you referring too probably reference ATC procedures for incoming traffic rather than restrictions on pilots. For example which controller is responsible for which airspace.
Like you said Class B airspace is typically airspace over crowded airports and is more restricted than most types of airspace.  When approaching this facility you will often be directed to "Approach" which is the actual TRACON. You may be handed off to different controllers as you transit the class B airspace.
I hope this answers your question.

You may want to address the difference between an approach and an arrival, since that seems to be a key piece of the puzzle that the person asking the question is missing.

I may be onto a piece of the puzzle. For example p.4 from this document describes Airspace delegation (I know the source is for simulation only, but there is a corresponding official document with very much similar information). This delegation is only to assign a controller to each sector, i.e. who will assist with approach procedures? If someone is outside Class B but within a TRACON sector (they have different upper altitude limits), can they simply continue flying by, or is this sector airspace dedicated to arrivals/departures as well?

Vector, the person can continue to fly-by and may not necessarily by in contact with ATC at all as mentioned by the other answer.  However, if an aircraft is flying IFR and is descending into or climbing out of Class B airspace the TRACON could be responsible for them outside Class B airspace boundaries.  This is common for commercial aircraft traffic.  Pilots are advised when to change to TRACON by ATC.  However VFR traffic who are not in contact with ATC must contact the approach frequencies listed on the chart and get clearance before entering Class B airspace.

There is no TRACON airspace—well, there is, that's why OP is confused. There is regulatory airspace (Class A/B/C/D/E/G), and there is airspace owned by a certain facility (of which the majority by volume will be Class E, in all likelihood, but could also be any of the other airspace classes). From a pilot's point of view, nothing changes from a regulatory standpoint and very little changes from a services-provided standpoint when one changes from ARTCC-controlled airspace to TRACON-controlled, or vice versa.

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text:
What does the indication "ATC" in some Take-Off Minimums mean?
While studying FAA's Standard Instrument Departure Procedures, I came across the La Guardia Five Departure SID. Take, for example, the Take-Off Minimums for runway 13L:

Rwy 13 (Coney Climb): 400-2 or Standard with minimum climb of 280' per NM to 500. ATC climb of 900' per NM to 1500.

How should I interpret this "ATC" indication? What difference does it have from the previous minimum climb gradient requirement ("climb of 280' per NM to 500") which omits this particular indication?

I believe I have found the answer to my own question, while examining the records of a meeting held by FAA concerning this subject ( source ). It clearly states:

[ AERONAUTICAL CHARTING FORUM Instrument Procedures
  GroupMeeting 17- 02 –October 24, 2017 ]
  When ATC crossing altitude restrictions require a climb gradient on a SID, it is proposed to establish a single climb gradient that would allow compliance with all ATC restrictions. These climb gradients would be
  identified on the chart as ATC climb gradients. Rich explained how the aircrew should treat each climb gradient differently. An obstacle climb gradient should be treated as a plane that the aircraft cannot ever penetrate from above, that is, the aircraft must always remain above the climb gradient’s surface. Conversely, an ATC climb gradient only represents the average gradient needed to meet the crossing restriction at the fix where it’s established. In this case, the aircraft’s altitude between the point where the climb starts and the point where the altitude restriction is established is not that important, provided the crossing is made at the fix at (or above) the minimum charted altitude. The purpose of the ATC climb gradient is to inform the pilot of the necessary performance needed to comply with the altitude restriction. The working group suggested that a SID should be limited to one obstacle climb gradient, and if necessary, one ATC climb gradient. Further, an ATC climb gradient and the associated crossing restrictions should be eligible for cancellation by ATC when not needed or when aircraft performance is limited.


text:
Does the term track guidance apply only to conventional procedures?
In ICAO's 8160 "Aircraft Operations" manual there is a term called "track guidance", for which I can not find any clear definition.
A few examples:

Departure Procedures 3.1
3.1.1 There are two basic types of departure route: straight and turning.
3.1.2 Track guidance shall be provided:
a) withing 20.0 km (10.8 NM) from the departure end of the runway (DER) for straight departures; and
b) within 10.0 km (5.4 NM) after completion of turns for turning departures.
3.1.3 Surveillance radar may be used to provide track guidance.

..

3.2.2 Types of Straight departure
b) straight departure with track guidance:
1) facility ahead or behind; and
2) offset (track parallel/track offset/track crossing).

..

1.6 TRACK GUIDANCE
1.6.1 Track guidance should normally be provided for all phases of flight through the arrival, initial, intermediate,
  final and missed approach segments. When track guidance is provided, the appropriate segment shall lie within the
  established coverage of the navigation facility on which the track guidance is based.

Judging from the context in which track guidance is mentioned, I would say that it refers to conventional navaid-based procedures, where the aircraft needs navaid facilities in order to keep on track.
All things considered, does the term track guidance have any meaning for RNAV/RNP procedures? Are RNAV/RNP procedures considered procedures without track guidance?
Any clarification would be appreciated.

ICAO Doc 8168 "Procedures for Air Navigation Services - Aircraft Operations - Volume I - Flight Procedures" states under 2.1.3 Types of SID:

Track guidance may be provided by a suitably located facility (VOR or NDB) or by RNAV.

To answer your question: RNAV/RNP SIDs are considered procedures with track guidance.
The better your tracking is the smaller the protection area required (especially for turn construction). So flying inbound or outbound a navaid or having RNAV capabilities greatly increases your precision und therefore allows for procedure construction with relaxed climb gradients in areas with difficult obstacle situation.

Thank you Chris, I appreciate your input! Just one small clarification: If both conventional and RNAV/RNP SIDs are procedures with track guidance, then under what circumstances is a procedure considered procedure without track guidance? Could it be eg SIDs with vectoring?

@VectorZita "without track guidance" simply means that you have no indication in the cockpit which tells you your deviation from the intended track. Something like a SID "At 800ft turn right heading 090. Intercept and proceed on R180 XYZ-VOR." The altitude and heading portion has no track guidance. The altitude depends on your aircraft performance (high or low rate of climb). The track flown resulting from the heading is heavily dependent on the wind. So these parts are considered to be "without track guidance". The radial is a form of track guidance so there the smaller safety zones apply.

In other words, even if RNAV/RNP SIDs are considered procedures with track guidance, in special cases like a VA leg of a departure procedure, these "special" portions of the RNAV/RNP SID have no track guidance? Because the definition of a VA leg is "heading to an altitude".


text:
Is the arrival segment of an IAP in PANS-OPS the equivalent of FAA's feeder route?
In ICAO's manual 8168 ("Aircraft Operations"), the term "Feeder route" is never mentioned. Instead, it states:

8168 Volume II, "Approach Procedures": 1.2.3. Segments of the approach procedure. An instrument approach procedure may have five separate segments. They are the arrival, initial,intermediate, final and missed approach segments.

My confusion concerns the difference between the arrival segment and a STAR. Does the arrival segment imply that it is also part of an arrival procedure, or is it just the equivalent of a feeder route, which is mentioned in FAA's TERPS?
Could someone help me clarify this?

An arrival segment can be part of both an arrival route and a designated STAR. Both are protected with the same design criteria.
The STAR chart consist of designated routes linking the approach procedure with ATS-routes or exit points in Free Route Airspace (FRA). An arrival route is simply a collection of arrival segments which are not part of a STAR when it is not operationally necessary to publish the route using the STAR criteria in ICAO DOC 8168 Vol. II Part I, Section 4, Chapter 2. The non-STAR arrival routes are published on the Instrument Approach Chart (IAC) as part of the Instrument Approach Procedure (IAP).
Here is an example from the Norwegian AIP:

The dotted lines from AND, SJA, FS and EVD to the IAFs are arrival routes containing arrival segments. These are the eqvivalent to feeder routes in TERPS, as they are defined equally.


text:
What are the risks to balloon flights in IMC, other than mid-air collision?
What are the risks to a balloon that enters IMC conditions? Mid-air collision with other IFR traffic seems obvious. What are the other risks? It seems like losing control because of losing track of what direction is "up" is unlikely compared to an airplane or helicopter.
I assume most balloon pilots have GPS and a map that lets them track the elevation of the terrain under where they are (and where they are headed) and avoid some hazardous places to end up (middle of a substation comes to mind).

"It seems like losing control because of losing track of what direction is "up" is unlikely compared to an airplane or helicopter." -- right, thanks to buoyancy

Of course the use of a GPS in a balloon can tell you what's ahead, but if you can't avoid an obstacle/terrain by going up (or down perhaps??) then you're going to hit it.

@DaveGremlin But that would be a general hazard to balloon flight, not specific to IMC, right?

Incidents in NASA's Aviation Safety Reporting System mention sudden low-level fog surprising pilots for various reasons.  Because nearby terrain is not visible, the risk then is not finding a safe landing area before fuel exhaustion (for a hot air balloon, not a much rarer lighter-than-air craft).  That of course risks damage to the vehicle, its occupants, and whatever it lands on.
As you guessed, these reports mention using GPS, a map (or familiarity with the local terrain), and communication with people on land, to navigate to a safe landing area.
http://www.37000feet.com/report/289605/Hot-air-balloon-flight-VFR-in-IMC
http://www.37000feet.com/report/338771/hot-air-balloon-pilot-took-off-in-IMC-conditions-then-climbed
http://www.37000feet.com/report/408264/Hot-air-balloon-pilot-landed-in-IMC-conditions-caused-by-fog
http://www.37000feet.com/report/910306/Hot-air-balloon-pilot-reports-entering-IMC-inadvertently-shortly-after-takeoff-and

Obviously if you are not short on fuel you could just go up through the fog / cloud till you break out and then let the wind carry you to a safer location where the ground is visible -- since knowing "which was is up" is not really an issue in a buoyance-based aircraft

Disorientation and spiral dive would be quite a feat, yes!  But fuel reserve was mentioned in at least one of those reports.  And the wind might carry you to a less safe location.

"the wind might carry you to a less safe location" isn't that a hazard inherent in all balloon flights?

Of course!  "Less safe location" only to counter the previous comment's "safer location."


text:
What problems do you start run into when an aircraft is disproportionally long?
For example, lets say we design a plane with the same lengh as the A340-600, but has the width of an embraer erj-140. Assuming everything works, what problems would we run into in regards to aerodynamics?

the problems would be structural, rather than aerodynamics.

Don't all missiles look that way?

If one assumes everything works then doesn't that mean that all problems including Aerodynamic are already taken care of..?

@Federico Most missiles do, in fact, have lifting surfaces referred to as wings in some literature. Not all of their lift can come from the slender body.

The question reminds me of the DC-8 Super 61. I always found its fuselage to be absurdly long (picture below, source).

Friction drag
First of all, your volume to surface ratio will suffer. A more slender fuselage will have proportionally more surface area for the same volume than a more stubby one. The first aerodynamic effect, thus, is a higher friction drag relative to fuselage capacity. Below a fineness ratio of five, increasing flow separation will unduly increase drag. Moving from an A340-style fuselage to something more slender, however, will not affect separation.
While volume would need to be held constant in case of airships, the goal for an airliner should be to maintain seating capacity, which can be assumed to be proportional to floor space (within limits - aisle height should not drop below 6 ft). Therefore, the figure of merit should be volume$^⅔$, and the growth in skin friction drag (and structural weight) should be less severe with increasing slenderness of the fuselage. Also, with a longer tail the tail surfaces can be made proportionally smaller, which reduces friction drag a bit, too.
The graph below is from S. Hoerner's Fluid Dynamic Drag, figure 24 of chapter 13, and actually valid for flying boat fuselages. It shows nicely how the drag coefficient grows with increasing fineness ratio; however, since the drag coefficient is based on frontal area, this is slightly misleading.

Hoerner's comments to this graph include an optimum based on volume$^⅔$:

The optimum ratio with respect to drag on frontal area, seems to be in
  the vicinity of 5. Based on (volume)⅔, a minimum drag coefficient is
  obtained at l/"d" ≈ 9, corresponding to l/b ≈ 15 in the hull family
  tested

Maximum Cruise Speed
When being operated at speeds approaching Mach 1, the more slender fuselage will show a higher value of the drag divergence Mach number, so the second aerodynamic effect of a more slender aircraft is a slightly higher cruise speed, wing aerodynamics permitting.
Again, a graph from Hoerner's Fluid Dynamic Drag (figure 37 of chapter 15) as proof:

Pitch Damping
Third, since the fuselage length will determine the lever arm of the empennage, a more slender fuselage of the same capacity will exhibit a higher pitch damping relative to its static stability. Pitch damping depends on the square of the tail's lever arm while static stability grows only linearly. Note that the tail size needed for the same stability and pitch authority will change inversely to fuselage length, offsetting some of the increase in zero-lift drag of the longer fuselage.
Take-Off and Landing Speed
If the landing gear remains unchanged, a fourth effect could be a lower rotation angle on take-off and pitch attitude on landing in order to avoid a tail strike. This might result in higher take-off and landing speeds.
This answer would be much longer if aeroelastic and structural considerations would be included. I restricted it to aerodynamic factors as requested.

"The first aerodynamic effect, thus, is a higher friction drag relative to fuselage capacity." Yes, but that is because fuselage capacity goes down more than friction drag. Aerodynamically, the ERJ diameter fuselage has less drag than the A340 diameter one because the wetted area is less. Also, a longer aircraft needs a longer landing gear no matter what the fuselage diameter is.

@Koyovis: Swapping fuselages would result in a pointless comparison. I understood the question such that the new fuselage should fit the larger A340 wing, thus be much longer. Now it does have a greater wetted surface and the comparison is less pointless.

Aerodynamically there would not be much of a problem. Maybe aeroelastically, because of the thin tube bending when elevator and rudder inputs are generated. But there are definitely structural problems.
When flying, the wings support the aircraft and the fuselage hangs off of them. A long, thin tube wants to bend down at the ends: tension at the top of the tube, compression at the bottom. The more distance between top and bottom, the lower the stresses and strains are and the lighter the construction - but our long thin tube has relatively little distance and we're creating a heavy and flexing construction.

There is a study on the resistance of the pipe (=fuselage in this case) to bending forces, as a function of the diameter and wall thickness.
From this study seems that larger diameter (given the same wall thickness) makes the pipe more resistant to bending. Also, when such a pipe finally bends, it is more likely just to buckle rather than failing catastrophically at the single point.
This probably explains why bigger airliners are made wider and higher (two levels) rather than just longer.

It does, there's an optimal proportion. Too thin and the structure bends and is heavy, too fat and the drag is high.

Buckling is merely the first step in the process of failure. A buckled structure will endure lower loads and exhibit larger peak stresses, so it will crack sooner.

Thin pipes (and with thin walls) tend to fail bending immediately and a lot at one single point that becomes kind of "joint". Wider pipes with thicker walls may initially bend less and over whole length. But the typical fuselage is probably strong enough to stand also against this kind of failure. I  have checked the history of known structural failures but tail and wings seem failing first. It must be an unusual plane, very long (as asked), for this to be a problem.

@knovics, you mean width  as in fuselage diameter or include wings and engine mounting geometry too? Maybe this answer is at cross purposes to the question, but a long airplane can have advantages too . . it provides a greater 'moment-arm' for the rudder and this can actually help to control the yaw during engine failure. Such airplanes have much lower minimum control speeds, Vmc. The engine failure on takeoff technique and calculation is predicated on the "use of aerodynamic controls only".
Shorter body airplanes can have issues on account of this, especially as engines grow, and thrust grows, and due to this they sometimes have a minimum takeoff weight limitation. Cases in point being the B777-200LR (length 212ft) and the B777-300ER (length 241ft). In such case, the longer (= larger, heavier) airplane will most likely also have lower landing speeds.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Bypass ducts and spinning blades
I want to start out by saying these questions will make me look a fool but i simply haven't found answers for them anywhere so i'm hoping you could help me!

What is the purpose of bypass ducts? If the air is going around the turbine then what even is the point? Why not just make jet engines simple consisting only of the turbine and skip out on the bypass duct?
What makes the fan blades in a jet engine keep spinning? I know how they are started but what keeps the blades constantly spinning with enough inertia to keep compressing air? Is there like a small motor connected to the fan blades via a crankshaft or is a portion of bleed air used to keep the blades in motion?

Thanks in advance for answering my questions :)

for 1. did you have a look here https://aviation.stackexchange.com/q/24536/1467 ? for 2. you can start here: https://aviation.stackexchange.com/q/25916/1467

Yeah then it's a turbojet not a turbofan or jetfan. Turbojet has bad fuel economy in the sub sonic range compared with turbofan and jet fan. Essentially the nozzle only is not the most efficient device to convert thermal energy to thrust. 2) Not a portion bleed air, but all of the exhaust gas.

My lord, I didn't know you were interested in aviation! :P

Well, let's tackle the second question first: What keeps the fan spinning? It is connected by a shaft to the low pressure turbine and the gasses expanding from the high pressure turbine towards the outside keep it spinning. Look at a good diagram and you'll see two (or three) concentric shafts that connect the low pressure turbine and the fan and the high pressure turbine and the compressor.
As for why bypass, pure jet engines where all the air goes through the combustors are really fuel hungry. You have to have a certain air/fuel ratio to get combustion. You can't lean it beyond a certain point or the fire goes out. Using all the air would use really a lot of fuel. The high-bypass ratio turbofan only takes some of the air through the combustors and just sucks the rest in with the fan and blows is out the back. The difference between that and a turbo-prop is mostly the cowling around the fan.


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What kind of cable is used to transmit signal from flight control computers to actuators?
I am a student and have been researching about ARINC 629 and AFDX. In b777 fly-by-wire system, what kind of cable is used to transmit analog signal from Actuator Control Electronic (ACE) to the respective electrically-controlled actuators? What kind of bus cables/connectors are used in ARINC 629?  What about in AFDX? Does AFDX use fiber optics?

If you specify analog signal it probably won't be fiber. Are you sure it's really analog?

ARINC 629
From The Avionics Handbook, chapter 11, Boeing B-777, Fly-By-
Wire Flight Controls:

The ACEs [Actuator Control Electronics] and PFCs [Primary Flight
  Computer] communicate with each other, as well as with all other
  systems on the airplane, via triplex, bi-directional ARINC 629 Flight
  Controls data busses, referred to as L, C, and R. The connection from
  these electronic units to each of the data busses is via a stub cable
  and an ARINC 629 coupler. Each coupler may be removed and replaced
  without disturbing the integrity of the data bus itself.

Triplex, bi-directional ARINC 629 Flight Controls data busses
Triple: The B777 has A629 buses that can be dual, triple (flight controls) or quadruple (engine controllers) for redundancy. A triple bus means the information is send on 3 buses in parallel, using 3 bus interfaces, like this:

Source
The primary flight controllers have three lanes allocated to different functions: command, monitor and standby. Each lane is connected to a different bus of the triplex.
A629 is in many points similar to thin Ethernet (e.g. 10Base2) but uses a twisted pair instead of coaxial cable for the physical layer:

Bi-directional: Contrary to A429, A629 is bi-directional, data can travel in any direction,
From any interface to any other interface,
The bus is a twisted cable,
Terminators are fitted at both sides to prevent signal reflection and stationary waves,
A stub connects the unit to the bus using a coupler,
Couplers are plugged directly on the cable without cutting the wires.

Source
Coupler: This is actually a transformer and data are transmitted by induction.

Source
Data: Data on the bus are digital, coded with Manchester bi-phase.
AFDX
AFDX (Avionics Full-Duplex Switched Ethernet) is similar to 802.3 Switched Ethernet Standard. The physical layer can be a shielded twisted pair or an optical fiber.
Instead of a bus topology it uses a star topology. Switches are used to connect the different nodes.

Source
The particularities of the switched network:

Data don't flow to each units on the same bus, the network can be segmented to reduce contention (collisions).
Since the broadcast domain is reduced, this allows for higher data rates.
Deterministic transfer times can be achieved, something which is important in real time applications.

AFDX also allows for virtual links, that is defining a point to point virtual circuit, to completely abstract the network layer.

Good answer but you didn't answer the "what kind of cable is used to transmit analog signal from ACE to the respective electrically-controlled actuators?" The analog signal cables depend on the signal type. Discrete signal I/O is typically a single wire. Voltage differential signals (proportional control) is typically shielded or unshielded twisted pair. UTP is preferred to reduce weight, but STP may be required depending on frequency response and potential interference.

@Gerry: ah yes indeed, I missed completely the part between ACE and PCU (I had this page bookmarked, likely because I wanted to update it, but see the bookmark only today!). The analog connection is multiwire, here is the connector on one of the rudder actuator. In addition of the position, there are wires to select the actuator mode, and for feedback (power metering and cancellation of actuators fighting against each other).


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Why don't airliners use crescent wings?
The crescent wing design seen on the Victor bomber seems to have a great number of advantages...

the critical mach remains more constant along the span, so the formation of shock waves is more even and has less pitch trim changes at high speed
higher inboard sweep at the point where the wing is the thickest increases the overall critical mach and thereby improves transonic performance
the curvature (somewhat?) reduces spanwise flow, thereby lowering tip-stall effects at low speed
when such a stall does occur, it happens at a point closer to the MAC, so the magnitude of the pitch-up is lower
because of the geometry of the approach, some designs will have a natural flare built-in - this was a major positive benefit on the Victor, although not a design goal

So... with all of these advantages, why doesn't everyone use them? Is there some disadvantage that is not being mentioned?


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Do any airbridges move vertically to match arrival/departure halls?
One of the things that always baffles me is that airports almost always have the arrivals and departures sections on different levels, but that you exit the aircraft into the departures hall. In some airports this leads to long walks along labyrinthine corridors to customs.
Now it seems to me that one could easily raise and lower the other end of the bridge to match the hall being used. Domestic flights could exit directly onto the arrivals level, and international to the customs. Yes, this would increase the complexity of the bridges, but much less than the reduction in complexity of the rest of the airport layout while eliminating many escalators and elevators.
Does anyone know an airport that does something like this?

You don't exit to the departures hall, you exit to the transit area. Some people are not leaving the airport, but going to a connecting flight, so they just cross this area to the other gate. Only those who end there proceed to the baggage claim and customs and border control.

Jetbridges are designed to move vertically to adjust to the height of the aircraft, not the building. The jetbridge would then need two vertical height drive mechanisms and would have to be long enough so to avoid excessive slope problems.

JFK's Terminal 7 (British Airways Terminal) had (no more) some gates with this feature. The terminal-side of the bridge moved vertically down for disembarkation, and up for boarding. You can see a photo in this post on flyertalk.com. Below is a comparison for the old/new systems:

Oslo doesn't have the exact same feature, but has escalators and lifts as part of the gate to lead arriving passengers to the transit area. From there they either proceed one floor down to the departures area, or two floors down to customs, baggage claim and the arrivals area.


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Are canards actually more efficient?
Another post here triggers this question;
Since I was a kid I have read endless articles about how canards are more efficient because both wing-like surfaces are lifting, whereas a tail surface is adding weight.
Yet the most efficient aircraft, gliders, almost never use this layout. A few have, Solitare for instance, but obviously this claim is oversold given the complete dominance of conventional layouts.
So what’s the story here? Is it that they are more efficient but some other effect makes them unsuited for most roles? Or is it simply not true in practice?

No. It's not true in practice.

While the conventional layout puts the whole tail into the downwash of the wing, a canard will add downwash to the center wing and upwash to the outer wing. This means that while the tail of a conventional layout sees less angle of attack variation than the wing (which is good to prevent tailplane stalls), the up- and downwash variations with varying angle of attack will spoil the lateral lift distribution on the main wing of a canard airplane and increase its induced drag.
Since the canard surface needs to fly at a higher lift coefficient than the wing for natural stability, it will have less margin for control. It is no coincidence that successful canard designs are unstable. Also, this means the big wing surface cannot be fully used for lift, which is wasteful and increases take-off and landing speeds.

More on this can be found here.

Since I was a kid I have read endless articles about how canards are more efficient …

The reason for this is simple. It is much more exciting for authors to claim they know better than all the experts than to humbly admit that the state of the art is really the best under the circumstances. The incentive to laud canards above all else is much too enticing, and human psychology tends to prefer the sources which confirm a preconceived opinion. In the end the authors really think they have found a better solution and become evangelists for a better world, especially when their own understanding of the matter is limited.

On the whole a canard does not lead to greater efficiency. However its aerodymanics are complex and little about it is obvious. Pretty much any statement can be - and often is - contested.
Yes a canard will be used to lift the nose during takeoff, helping the main wing instead of adding to its load. Since liftoff is the highest-loaded yet slowest-moving moment in the flight, this does genuinely help wing loading and therefore size and weight, making the airframe overall more efficient.
But in a basic arrangement, for a plane to be stable the forward surface must be loaded more heavily than the rear. On a canard the main wing is therefore loaded below its maximum capacity, which means that it must be oversize and much or all of the above saving is lost. On a tailless type, the wing must similarly be made overlarge so that the rear surfaces can act as the tail (through either reverse camber or, if swept, tip washout). On the other hand of course, both canard and tailless avoid the need for a long empennage hanging out the back.
Fitting a high-lift canard so that the wing can work harder after all leads to safety issues such as the wing stalling and dropping while the canard still holds the nose up, and suchlike. It has generally proved too unsafe to put into production.
The canard's downwash will also tend to mess up the oncoming airflow for the wing, and that mess changes under different flight conditions such as speed and angle of attack, so the wing must have a good safety margin to tolerate such disturbances. That means more inefficiency.
However canards can provide performance efficiencies at high angles of attack by helping to manage the airflow over the main wing, in say a dogfight or when taking off and landing.
In most situations a canard works out more trouble than it is worth, either inefficient or dangerous. But there are exceptions.
The first two successful man-powered aircraft, the Gossamer Albatross which won the Kramer prize and the Gossamer Condor which crossed the English Channel, were both canards. Interference with the wing was much reduced by the low Reynolds number of the canard at its very slow cruising speed. It was also set physically lower, so that the wing passed over rather than through its downwash. So just because the canard is not worth it for sailplanes does not mean that it is inherently inefficient for all low-speed applications.
Several later variants and local modifications of the classic Dassault Mirage III tailless delta fighter were noticeably improved by adding canards. Although less efficient in cruise, at high AoA the canard improved the airflow over the wing to generate extra lift which outweighed the extra drag,   improving its efficiency under such conditions. This made it more efficient in a fight for example, with the extra lift allowing the plane to hold altitude better during a tight turn.
Ultimately, if canards were less efficient when and where it really matters, they would not have been chosen for so many 4G/5G combat aircraft, such as the Eurofighter Typhoon, Dassault Rafale and Saab Gripen.

Human-powered airplanes fly at only one speed and altitude, so the interference between canard and wing can be taken into account. Not so for all other types of airplanes (OK, except maybe for HALEs which also fly at only one speed), where the changes in angle of attack will vary interference and often spoil efficiency.

@PeterKämpf On the Condor and Albatross, things got more complicated in a turn, as the canard was canted sideways to act as a fore rudder, and this changed its flow pattern differentially with respect to each wing. The Albatross was also subject to significant gusting and accompanying dynamic flow effects during parts of its flight. Nothing with canards is ever simple.

Well for example for the JA-37 the canards do not produce a lot of lift. They do however produce a vortex that passes over the main wings which in turn makes the main wings lift greater. That also allows for higher stall AoA point and shorter take-off distance. They do increase drag and weight though, so there is downsides to having them.
On more modern aircraft where canards can be rotated they can also double as speed brakes and probably increase pitch moment too making the aircraft more agile.

Yes, but it is hard to get the right ones which will have minimal impact on the  areas of the main wings. One advantage for using canards (not planes with three surfaces like the Sukhoi Su-37) is that the tyres aren't pushing down into the runway on takeoff like with conventional aircraft, which have to produce downwards force at the back to lift the nose. They also have more agility pointing the nose during manoeuvring. However, they do reduce the downward field of view of the pilot.


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What is the type of a SID that is neither RNAV nor RNP?
I am studying FAA's Order 8260.46F and I have noticed that, as far as the different types of SIDs are concerned, it states:

[3-5] (1) “RNAV 1” will be the default designation for RNAV DPs. Annotate procedures with a standard note: “RNAV 1” on Form 8260-15B [see appendix E].
  (2) “RNP 1” (in-lieu-of RNAV 1) will be used when a DP that contains an RF leg or when surveillance (Radar) monitoring is not desired for when DME/DME/IRU will be used. Annotate the procedure with a standard note: “RNP 1” on Form 8260-15B [see appendix E].
  (3) All RNAV DPs will contain a note that describes the equipment sensor limitations.

However, I have trouble figuring out what type of SID is the La Guardia Five Departure ( route description and take-off minimums ) of La Guardia airport. It is does not have the indication "RNAV" and, as far as I can tell, it is not an RNP departure procedure either.
Could someone point me in the right direction?

That SID uses conventional NAVAIDs- the additional pages have the textual description of the route.

@sbooth thank you for your comment. Could you help me a bit more to clarify this? When you say that it uses conventional NAVAIDs, does this mean it is an RNAV type of SID? If not, then how would you call this type of SID?

That SID is not an RNAV SID since it uses VOR/DME and headings for navigation. The FAA Aeronautical Chart User’s Guide simply refers to them as “non-RNAV SID’s”


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Phoenix Area Helicopter ATC: What is "Hee-lah" (Gila?) One, and what is the 101 transition?
I've been listening to the Phoenix Tower LiveATC feed, and I hear references to "Hee-lah" (Gila?) One and the 101 transition with helicopters (see audio files below):
Angel-Five
TV-3
TV-15
Does anyone know what these are? References would be appreciated if possible. Thanks!

I have all IFR procedures on my iPad and cannot find a SID or STAR into or out of PHX with a similar name.  Is the airport Phoenix Sky Harbor?

Yes, Phoenix Sky Harbor. I looked on Airnav and on Skyvector and couldn't find a departure chart with "HELO" on it. I also checked the TAC chart and didn't see anything.

Are these recent recordings?

You should be looking for Gila. It's the name of a highway, a town, a monster and who knows what else. and 101 is a freeway both east and west of Sky Harbor.

Has anyone gotten a good answer on this? I too was listening in on KPHX North/South tower frequency and heard a number of helps request and be cleared for a “Helo-1” route....or possibly a “GILA-1” route VFR

Re --"You should be looking for Gila. It's the name of a highway, a town, a monster and who knows what else"-- definitely a river.  Also a native American reservation/ community.  Both in the Phoenix area.

The Gila is a river that runs through Arizona, so that may be a visual reporting point for incoming aircraft.

Through Arizona and, more specifically, through Phoenix!

The Helo One is a Helicopter only special signatory and training required ATC procedure that provides procedural access to the PHX class B airspace.
It is not a published procedure. You must have been briefed and signed an LOI with the TRACON (not the tower). It is not an IFR procedure, and it is not listed in NAV programs. Its not a route either. Its is purely an authorization to operate in the PHX class B.
Transition areas are provided for helicopters to cross under the final approach paths providing proper separation from Sky Harbor traffic with little or no radio traffic requirements once contact and clearance is obtained. There are east/west transition areas on the north and south sides of the airport as well.
If you are listening on radio you will hear all north-side users on the TWR frequency for runway 26/8 and all south-side users on the runway 25/7 TWR.

Would that be an LOA (letter of agreement) instead of an LOI (letter of intent). Or does LOI mean something else?

I have been unable to confirm this as I can't find any helicopter specific charts for the area, but I think they are asking for the HELO one route and the 101 is apparently a major highway in the area and probably a local vfr reference point.
Bigger airports may have separate published helicopter routes to arrive and depart helicopters away from the pattern traffic.

There was once a GEELA STAR. I can’t find a good image of the chart for it, though. In 2013 the FAA did an optimization of theMetroplex airspace, the result of which was that the GEELA STAR was replaced by the HYDRR STAR.
If you look at the frequency information on the Airnav page for KPHX you will see that there is a frequency assigned for the GEELA STAR. I can only speculate that ATC might still use GEELA informally for helicopter traffic.

GEELA is the waypoint after HYDRR on the HYDRR STAR. However, the OP's first audio clip was for a departure, so it doesn't make sense that they'd be referring to a STAR.

@StephenS It's not exactly a departure. They're coming from heliports west of the airport, passing through the terminal area to destinations on the east side. I find no evidence of there being any published helicopter procedures. Although GEELA STAR is no longer published as such, they still list a frequency for it, so it must be still used for something. It's all a guess, really


text:
Why would ATC issue a takeoff clearance and also tell the same aircraft to maintain visual separation at the same time?
I heard this from the Phoenix Sky Harbor airport tower years ago on a sunny and hot day.
Is it because the controller is able to take off aircraft more quickly by putting the responsibility on pilots to maintain separation, rather than use the standard separation requirement if ATC does it?

Check this one out:  https://aviation.stackexchange.com/questions/2949/what-are-the-pilot-responsibilities-for-maintain-visual-separation-clearances?rq=1

I don't have references, so will wait for a better person to answer, but you are correct.  This is common practice in Las Vegas too.

Yes, the Tower's separation standards are different if the following aircraft accepts the responsibility to maintain separation visually.  If the following aircraft can't (or declines the clearance to) maintain separation visually, the controller has to wait significantly longer between subsequent departures.
Typically, the transmissions from Tower are something along the lines of:

Tower: "Airline 123, line up and wait 25R, confirm A320 on departure roll in sight."
Pilot: Airline 123, line up and wait 25R, Airbus in sight.

After the A320 has rotated:

Tower: Airline 123, 25R cleared for takeoff, maintain visual separation on preceding traffic, they will be turning north.
Pilot: Airline 123, cleared for takeoff 25R, maintain visual separation on the Airbus.

The advisory to the crew about they will be turning north gives them the awareness that they won't be following the other aircraft for miles and miles, just until it reaches the point a few miles from the airport where some traffic turns north and other traffic turns to the south (or proceeds straight-out).  The aircraft will generally be sequenced by Ground Control so that they line up at the runway in a sequence such that the departure directions are staggered.  When this doesn't work, at PHX anyway, that tends to be when there is a break in the flow of departures for a minute or so, and during that time aircraft that have landed on 25L (in this case) and are waiting down-field to cross the departure runway, can cross and then taxi to the terminal.  Tower will often let the "waiting to cross" queue build up to three or four aircraft -- each holding short of 25R at a different taxiway -- while they launch departures rapidly, and then one departing aircraft remains "lined up & waiting" while the arriving aircraft are cleared in rapid sequence across the runway.
And after they're all clear, the departures resume.
All in all, it's a pretty efficient way to "move the metal" & get lots of aircraft into the sky as quickly as possible on clear days -- which PHX has plenty of!

Please don't use codeblocks to highlight or indicate quotes. It interferes with the accessibility of the site for some users. Either emphasis or quoteblocks should be used as appropriate.

Agree completely with your answer, although in my experience a better example would be a medium jet following a smaller slow aircraft (Piper or Cessna) since they can be slow to move out of the way. The benefit of using this procedure with two following jets is negligible since since they both move at similar speeds.


text:
What are the ICAO equipment codes for those Garmin units?
What are the ICAO equipment codes for those Garmin units?

Garmin G500 / 750 / 650 WAAS navigators?


text:
Height Loss In Descend with increase in altitude
Will the physical height lost in 3D would be same if I descend with 500 fpm from 2000 to 1000 feet compared to descend with 500fpm from 20000 to 19000

It's unclear what you're asking. Based on your current phrasing, the height difference here is -1000ft, the rate of descent is completely unrelated -- but that's just simple arithmetic, and not an aviation question.

No, the exact physical height loss will not be the same when comparing different altitudes because aircraft altitude is based on pressure altitudes and altimeter settings.
When you add local temperature and pressure differences into the equation, the altitudes will never be exactly 1,000 feet apart. That is one of the reasons why Air Traffic Control uses 2,000 foot separation above 29,000'.


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Regulations regarding cleaning of water cooking equipment on planes?
Inspired by this question over at MiYodeya, does anyone know of specific practices or regulations regarding the use and cleaning of water urns on commercial planes?
Specific questions would be

are water urns on planes only used for water?
are they washed? (or do we saw that they don't need to because they only contain water)?
are they washed in dedicated washing machines for water urns or with other food containers/dishes?

These might seem weird questions but some Jewish travelers who observe Jewish dietary laws (i.e., eat kosher) will decide whether they can drink coffee on planes based on these answers.

I'm pretty certain that there would be no regulations (as in, law) regarding use of dedicated washing machines for water-only containers. That would probably be up to each airline, and I wouldn't be surprised if there exist airlines that do, but I also wouldn't be entirely surprised if there exist airlines that don't care.

see one answer here

From observing catering operations as a passenger on many flights:

Hot water is served from the same pots as coffee, so that only one type of hot liquid container is needed per flight. The pots are clearly intended for hot water or coffee. This doesn't mean that the flight attendants haven't used it for something else. For example, the galley sink might get clogged and the flight attendant uses the pots as a scoop to move the liquid to the toilet. I've seen this at least once.
Yes, everything with food contact has to be washed and disinfected, especially on international flights for phytosanitary reasons. They even will wash the trolleys. They cannot disinfect the pots on the aircraft, so at the end of the flight, they are placed back in the metal catering containers, and will be washed in the catering facility with all other supplies ("rotables").
There's no regulation or non-religious reason why you'd want to separate the coffee pots from the rest of the equipment, so I doubt any airline does this. Here's a page showing pitchers being washed with serving trays and drawers.

In the majority of galleys, the hot water comes from the coffee maker or dedicated water boiler, which operates like a commercial coffee maker: there's a constantly heated internal hot water tank that is automatically refilled from the aircraft water tanks. My understanding is that it may be best to have hot water dispensed directly from the maker, since that is dedicated for water use.


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What is an "all-electric APU"?
Understand that the APS5000 used in the B787 is the first all-electric APU for large commercial aircraft.
Source: http://www.pwc.ca/en/engines/auxiliary-power-units
Sorry if this sounds too amateurish, but what exactly is an 'all-electric APU' and how does it differ from past traditional APUs? Does the design allow it to generate the higher electric power required for the B787 and more electrical aircraft?
Any help would be appreciated, thanks!

Usually an APU provides electricity and bleed-air, just like the aircraft engines do. An all-electric APU only provides electricity. This can be done in the Boeing 787 because of the bleedless architecture where systems that would normally require hydraulic or pneumatic pressure are fully electrified.

How does the 787 start its engines without ground power (or following a midair flameout at an airspeed too low for a windmill restart), then?

@Vikki-formerlySean, as long as one engine or the APU is running, the electrical power from that device can drive the starter generator to start an engine.


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Is it possible to 'retrofit' electric flight control actuators to replace existing hydraulic actuators on aircraft?
Read a bit about the potential cost savings of replacing existing hydraulic aileron actuators on large commercial aircraft such as the A350/380 with electrohydraulic/electromechanical actuators.
Airbus estimated that it achieved approximately 1,000 pounds of weight reduction on the A380 aircraft when a hydraulic aileron actuator is replaced by electrohydraulic or electromechanical actuator.
Source: http://mil-embedded.com/articles/motor-control-more-electric-aircraft/
Does anyone know if there are any ongoing efforts anywhere into replacing existing actuators with the 'more electric' EHAs/EMAs? Any insight is appreciated!

It's not fair to call EHA 'electric' flight control (in the title). They may be 'more' electric but still mostly hydraulic. For primary controls, purely electric/EMA controls are hardly feasible any time soon at all, let alone retrofitting them.

Technically it's entirely possible to replace these actuators but it's unlikely they will because the economics don't work out. The weight savings you get will be offset by the costs from design, recertification and installation. It's not as simple as bolting something on.
When you make a big change like this to an airplane you have to take into account the changes it will bring. The actuator may be a different shape, the loss of weight in one area will change the balance of the airplane and affect its structures in ways that have to be accounted for. The forces the new actuator design will put on structures must be accounted for.
Electric actuators need electricity, that means you need to generate it and supply it. You'll have to run wires for it, maybe change the engines generators so they supply more juice. You may have to change the Ram Air Turbine so control can be maintained if engine power is lost. The airplane's control systems may have to be modified. Emergency procedures, maintenance manuals must be changed, people have to be trained, etc. Finally, all this must be certified with the FAA, EASA, and other bodies before passengers can be taken, only then can the actuators actually be replaced.
All this costs a lot of money to do, which is why major retrofits like that are rarely done, the ton of weight they save isn't worth the costs of doing it, even over 10 years of flying.

Those new power wires also need fuses added to the fuse panel


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Why don't the ATR 42's propellers start/stop rotating simultaneously?
Why is it that for the ATR 42 one of the propellers begins to rotate before of the other?
I've noticed that they also stop rotating at different times. Is there a reason for that or is it just for turning left or right?

Pilot only starts one engine at a time so the battery doesn't have to spin up both at once. At turnoff, one stop button is pressed before the other.

Sometimes an airplane will taxi on one engine to save fuel as well.

Yeah, you start engines one at a time, unless it's a B-52, in which case you have a lot of engines to start and a very short time to get the heck out of Dodge...

Also the right engine may be running without propeller turning, because ATRs (neither 42 nor 72) don't have APU, so instead there is a propeller brake on the right engine, so it can be running without propeller spinning for power generation.

@Harper-ReinstateMonica  Reminded me of the Convair B-36: "Six turning, four burning".


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How can you calculate the required tailplane force to ensure steady state flight?
Consider a max forward and a max aft CG position.

Wouldn't it be easier if you just name the textbook and let us know which of your homework questions we should answer?

I wish there is a textbook for it.

Maybe this will help. https://courses.cit.cornell.edu/mae5070/DynamicEquations.pdf

Any flight dynamics or aircraft design text book can help you here.
Check out Torenbeek, Etkin or Roskam. Basically if all you need is the force required and not control surface deflection or tail size all you need to do is a moment balance about the aircraft CoG


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What is the relationship between EGT, Fuel Flow, N1, N2 and Air Temperature?
I initially wanted some sample data for EGT, Fuel Flow, N1 and N2 to build a prognosis system that predicts engine failure (ECTM).
I searched for some sample data online but got to know that there's virtually no way of acquiring that. (Where can I find sample data required for Engine Condition Monitoring?)
Now, I have to generate my own data for this. It is crucial for me to understand the relationship between the 5 important parameters that I'm taking into consideration.
Parameters are EGT, Fuel Flow, N1, N2 and Air Temperature.
For now, I've understood this:

Temperature increases, EGT increases.
Temperature increases, Fuel Flow increases.
N2 decreases, Fuel Flow increases. (src - What does it mean for N1/N2 to float?)

Can you guys please give me more insight like the ones above? Also, please correct my mistakes. I'm a computer science student and this is all very new to me.

Oh. I didn't know that. I've been reading about aircraft engines only since 2 days now. I'm only trying to generate some fake data to build an ECTM prototype. I'll keep this in mind when doing it. Thanks!

I am not really sure what sort of engine failures you want to predict, but ECTM is usually used to detect things such as;

Worn air seals
Blade tip wear (compressors and turbines)
Compressor fouling
Eroded blades and turbine nozzle guides

These hardware issues cause changes in the “state variables”;

N1 (LPC) compressor efficiency
N2 (HPC) compressor efficiency
N2 (HPT) turbine efficiency
N1 (LPT) turbine efficiency

These changes in component efficiency then result in changes of the engine parameters;

N1 rpm
N2 rpm
Fuel flow
Exhaust gas temp
etc.

By detecting changes in the measurements, ECTM aims to tell you which module (LPC, HPC, HPT, or LPT) has degraded. Usually, it’s not possible to say why the efficiency has decreased (i.e. you can’t tell if it’s erosion of the blade leading edge, or worn blade tips), you can only tell which module is affected.
But the relationship you want between changes of efficiency and the measured parameters, is very complex. For that step, you need a performance simulation program, to give sufficient accuracy if you are actually going to apply the approach to data from a real engine. Otherwise, all one can say is, when an engine degrades, fuel flow, temperature, and rpms will go up. And they go up for most (or all) of the faults above. So, unless you know how much they change for each fault, you can’t tell which module has degraded. Then, your method is just saying “the engine has degraded” (not so useful), rather than why (and, only the LPC needs a repair, for example, which is cheaper and quicker than an HPC repair, because it requires a lot more disassembly).
But, if all you want to do is test an approach in theory, you could just make up the increase in each parameter, it doesn’t have to be accurate, because it’s just a mathematical example, you are not going to apply it to an actual engine, so the predicted effects of degradation don’t need to match reality closely. Just make up 4 different patterns of degradation;

degraded LPC: 50 rpm N1 increase, 200 rpm N2 increase, 5% inc in fuel flow, 200 deg inc in EGT
degraded HPC: 100 rpm N1 inc., 200 rpm N2 inc, 7% in in fuel flow, 150 deg inc in EGT

etc...
Then, create multiple examples of each fault by add a random amount of noise to each parameter, say < or up to 1% of full scale value (and you can make full scale up as well, let’s say, N1 = 8,500 rpm, N2 = 12,250 rpm, fuel flow = 3.2 lb/s, EGT = 650 deg C.)
Now, you have examples with noise, of known faults. See how well your method can correctly find the faults....
Sure, it’s a little crude, but if you can’t get hold of a performance simulation program that lets you change the efficiency of the modules to generate the degraded fault behaviour, at least it lets you do something. You can play around with the numbers, and see what size enables you to detect a fault, and what size does it start to get confused/ wrong.

This is awesome! You compiled my 2 days worth research in one answer. This is exactly what I was looking for. What you said is exactly what I'm trying to do. I'm just adding some amount of noise to each parameter and trying to build my machine learning model around it. Its good to know that I haven't deviated too much from what I intended to achieve. Thanks again for this beautiful answer!

@ShreyasS.  Glad to help. Just to clarify, though I think you have followed my words correctly, when I say “add a random amount of noise”, I mean, create multiple examples of each of the 4 faults, with a random amount of noise on each example. So, say 100 examples x 4 faults. Machine learning is a good technique to try. Are you using Python, by chance?

Yeah, that's right. So for example, I've assumed the range of EGT to be between 700 and 1900. When generating random data, I've given the range to be 500 - 2100. Whenever EGT goes below 700 or above 1900, I consider it a fault. I've created 100,000 rows of data like that. And yes, I am using python. If you're interested, you can check it out on my github account - https://github.com/shreyas707/ectm


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Where can I find sample data required for Engine Condition Monitoring?
I'm trying to find some sample data required for Engine Condition
Trend Monitoring to analyse and predict when an engine might fail.
I went through a lot of research papers and (kind of) understood the parameters needed for Engine Condition Trend Monitoring. From what I've understood, I need Exhaust Gas Temperature, Fuel Flow, Low Pressure Fan Speed, High Pressure Rotor Speed, Engine Pressure Ratio and EGT Margin data.
I'm doing this as a part of my college project and I need some sample data to start working.
Also, please correct me if I'm wrong because I'm very new to all this.

Oh! Sorry, my bad. Should I delete the question?

No, don’t delete the question (it is still a good question).  A small change in phasing such as “what data is required for engine conditioning monitoring” fixes any issue moderators might have, so no need to make a drastic move.

Your list of parameters is on the right track, and is the minimum set. If you can add a few more temperatures and pressures at other “stations” within the engine, the diagnostic accuracy improves.
No one on the internet will send you real data. OEMs and operators don’t give out data, because it contains proprietary information. That’s why 90% of the papers you have read probably use simulated data. Also, with simulated data, you actually know what the fault was. With a real engine, you don’t because when you pull an engine apart, there is no simple dimension you can measure to tell you what the change in efficiency of the fan actually is, for example. But, the trick with simulated data is to add a realistic amount of noise.
To generate simulated data you need a gas turbine performance program, like GasTurb or GSP. The latter of these is free for personal use. Maybe if you google “gas turbine performance simulation software” you will be lucky and find something free that does enough for your research.

Oh, thanks! I'm a computer science student and so my knowledge about all this is extremely limited. I only started reading about aircraft engine today.
I'll search for free softwares and also see if I can find any mutual friend who works in the aviation industry. Maybe they will have access to the software. Your reply truly helped a lot. Thank you!

NASA has an extremely basic jet engine simulator available for free https://www.grc.nasa.gov/www/k-12/airplane/ngnsim.html  It's not anywhere near what a major OEM would use, but it's free and might get you started.

That's good to know! Thanks Daniel, I'll check it out.


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From how far away are the navigation lights of a large airliner typically visible?
I live about 22 miles away from one international airport in the UK, and just over 30 miles away from another.
When I spot aircraft lights at night and check for corresponding aircraft on flightradar, I'm surprised to see that they seem to belong to aircraft making approaches to land at these airports - which got me thinking - on a clear night, from how far away are a large aircraft's navigation lights typically visible? (I'd be interested in answers relating to distance when viewed from the ground and in the air).


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What is the correct procedure for overwing fueling a CRJ200?
I have a question regarding overwing fueling a Canadair CRJ200. Let's say I was pressure fueling and one of the wings started venting fuel on the ground. The Crew Chief determined that I had to overwing fuel the wings, and then finally the center tank.
My question is: exactly how much fuel in gallons can I load into each wing before I should move back to the other wing and start fueling? Meaning, what is safe so that there is no tipping of the aircraft after fueling one wing and then moving to the other to also save time from going back and forth more times than needed to achieve desired amounts in each wing?
Say the Right tank has 2450lbs, the Center tank has 0 and the Left tank also has 2540lbs. I have to start overwing fueling and the pilot's order was for 12,500 lbs total. How many gallons should I start fueling with in (say) the Right wing before I move back to the Left wing and then back to Right again etc.? And then then finish off the Center tank?

This sounds on first impressions like it should be covered in a manual somewhere?

Welcome to aviation.SE! I edited your question to (hopefully!) make it more readable but if I got anything wrong then don't hesitate to roll back or edit it again yourself. You might also like to take the [tour] if you're new to StackExchange in general.

Thank you very much for doing this and hopefully someone can answer this as I have been having a hard time finding out this question of overwing gallon fueling amounts and the aircraft possibly tipping?

Hopefully someone can answer, but it's very specific and sometimes we just can't answer those questions because no one here knows. If this is a real-life scenario then I guess that you could ask your Crew Chief or another supervisor/manager. After all, if this is part of your job, your employer should make sure that you're trained to handle it.

Thank you very much for your input, a pilot had told me that 2500 lb imbalance which equates to 375 gals should be the max to be able to fuel each wing safely before fueling the other side and so on.


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Is there a difference between MEA and MOCA within 22 nm of a VOR?
As we all know from our instrument training, the MOCA is:

MINIMUM OBSTRUCTION CLEARANCE ALTITUDE (MOCA)- The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments which meets obstacle clearance requirements for the entire route segment and which assures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR.

Whereas the MEA is:

MINIMUM EN ROUTE IFR ALTITUDE (MEA)- The lowest published altitude between radio fixes which assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes. The MEA prescribed for a Federal airway or segment thereof, area navigation low or high route, or other direct route applies to the entire width of the airway, segment, or route between the radio fixes defining the airway, segment, or route.

(Both quotes taken straight from the Pilot/Controller Glossary)
The only difference in language is the bit about 22 miles from a VOR.
Therefore, when you're within those 22 miles, there's no practical difference between a MEA and a MOCA, right?

If that's true, why is there an 1800 foot difference between the MEA and the MOCA within 22 miles of the PMM VOR on V84?

You are right. Within 22 nautical miles of the VOR, there is no practical difference between an MEA and a MOCA.
However, it should be noted that the 22 nmi is only a limitation if navigating via VOR's.
14 CFR - CHAPTER I § 91.177  Minimum altitudes for IFR operations

(a) Operation of aircraft at minimum altitudes.
  Except when necessary for
  takeoff or landing, or unless otherwise
  authorized by the FAA, no person may
  operate an aircraft under IFR below—
(1) The applicable minimum altitudes
  prescribed in parts 95 and 97 of this
  chapter. However, if both a MEA and a
  MOCA are prescribed for a particular
  route or route segment, a person may
  operate an aircraft below the MEA
  down to, but not below, the MOCA, provided
  the applicable navigation signals
  are available. For aircraft using VOR
  for navigation, this applies only when
  the aircraft is within 22 nautical miles
  of that VOR (based on the reasonable
  estimate by the pilot operating the aircraft
  of that distance)

The MOCA provides "obstacle clearance requirements for the entire route segment," so if the applicable navigation signal is GPS, and you're receiving it, then you've met the requirements. This is why sometimes you see a MOCA on segments which aren't within 22 nmi of any VOR.
One other practical difference to keep in mind is that, especially in mountainous areas, you're much more likely to get radar coverage, and have better communcations clarity, at the MEA than the MOCA (I saw this a lot in Idaho). In those cases, ATC is probably going to prefer the MEA.

Then why is there an 1800 foot difference between the MEA and the MOCA when less than 22nm from the VOR?

@SteveV. Two things of note: 1. JYBEE (the change over point) is technically just barely more than 22nmi (22.1). 2. JYBEE is farther away from Keeler (ELX), which defines the intersection. So it's possible you wouldn't be able to determine the intersection where the MOCA changes using only VORs (no DME) at 2200. Though, reason 1 seems like the more likely explanation - even though common sense would indicate it is totally pointless.

You need to be at or above 4000 to ID CLAUD if using the cross radial (197) from the vor that is out of view , that is why a MOCA is there.

Are you sure you mean MOCA?  Usually that's what an MRA is for.


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What non-precision approach in the US has the longest segment at MDA?
What approach is the longest approach, in the US, which has the longest segment at the MDA?  Obviously this is for non-precision approaches.

Perhaps someplace with a really, really high MDA. Maybe Aspen or someplace like that where you need essentially VFR in order to expect to see the runway at MDA on a normal-ish descent? Interesting question.

The NDB/DME-A approach at KSUN has 5.2NM to fly visually from the MAP to the runway but I have no idea if that's the longest or not.

@Ralph J, actually, I was looking for low, but long MDA segments, but that was not the question.  My guess is that we will find 6 to perhaps 8 or 9 mile segments.  The answer to the normal question might be in TERPS, which I have not exhaustively searched yet.

Hmmm, don't have any solid answers. I'll toss out LDA 25 at KEGE http://155.178.201.160/d-tpp/1710/06403LDAD25.PDF as my effort, but I suspect others will find better answers than that.

That LDA  segment is over 7 miles. Great find, @RalphJ.  This will be a long search, or require some fancy data mining, unless someone has the right answers closer to their fingertips.


text:
Statistically, what are the failure points on sUAS (drone) aircraft?
It is generally recognized that operator error and unairworthy aircraft are the principle factor in sUAS (drone) system failures and accidents.  But looking just at the hardware, are there published studies on the aircraft systems components which cause the greatest number of system failures?
For example, batteries.  Or motors.
Has anyone done any kind of a large scale study of failures and published it?

Perhaps failure knowledge of traditional RC aircraft might lend some insight.

From own experience after leading a drone detection test campaign with over 500 flights of various drone types, the battery is a weak spot (sudden drop in capacity require early landing)  , electronic failures (either in radio transmitter or receiver, or on board electronics). In this series of 500+ flights we had one motor failure leading to 100m altitude loss. The drone then recovered its stability and then lost stability again shortly before landing. This was the only crash with extensive damage we encountered. Ina previous test we lost a drone due to an electronics glitch.


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Why is Iceland an efficient connection point between London and Boston/NYC?
Air connections thru Iceland (Keflavik) have been increasing explosively in recent years. Keflavik is used as a transfer point on trans-Atlantic itineraries.
The highest-traffic city pair involving Keflavik is Keflavik-London, so Keflavik is evidently being used as a way station between London and North America.
Also, NYC and Boston are the top North American routes for Keflavik.
However, Iceland is quite out of the way of the US northeast-London direct path. Why is it economical to stop over in Iceland, despite it being off-course?

Maybe Iceland is a nice place to visit and lots of people fly from (or through) London to get there? Also, it's not that far out of the way.

@GregHewgill most of the traffic thru Keflavik is connecting at this point

@the stop adds 320 mi. admittedly that is less than I thought.

One of the benefits of having a stop halfway is that the aircraft can refuel.
It therefor doesn't have to carry the fuel for the second half of the flight during the first half, which saves fuel.
The uplift of fuel costs approximately 4% of its weight per hour of flight. That means the fuel you consume in the 4th hour of flight has burned approximately 11.5% of its original weight, just to carry itself. The fuel burned in the 7th hour of flight has burned 25% of its original weight , just to be carried for the previous 6 hours. (which means you have to load 133% of the fuel used in the 7th hour)
So a 10% detour in distance, with an extra stop, does not increase the total fuel consumption much. It may even reduce the total fuel consumption of the flight.
And it also means that the aircraft is lighter, so it is more efficient to use a smaller aircraft. Typically you see mostly Boeing 777, 747, 767 and Airbus A380 and A330 across the Atlantic, but if you look at the traffic in Keflavik, you'll note that most aircraft are B757 and A321.
These aircraft perform well at mid-ranges, but on longer ranges they have to reduce their payload for fuel uptake for the long flight. For longer flights the bigger (and more expensive) aircraft are more efficient.
So the effect of the extra stop is that you reduce the fuel consumption, so that you can use smaller aircraft with lower fuel capacity which in turn means lower capital expenses. This makes the Iceland option economically attractive.

so comparable fuel costs, but cheaper planes (and smaller so easier to fill)

Iceland is a perfect transatlantic hub. Most importantly, it makes single connection flights efficient between nearly all European and North American cities. Fuel and equipment advantages have already been mentioned. Look at all the city pairs, not just LHR-NYC, and you'll see that it's better as a hub than London, New York or any other city located on the mainland continents.

It is part of a larger effort to boost Icelandic Tourism and has more to do with the economic condition of Iceland (of which tourism makes up 42% of their economy) than aviation for the most part. Iceland is a nation that does not have a huge amount of exports and relies heavily on tourism. Budget Icelandic airlines have been operating with Keflavik layovers and cheap flights (almost un-beatable prices) to and from Keflavik in an attempt to boost through traffic and encourage stays in neighboring Reykjavik. Both Icelandic Air and Wow air even offers a no-additional-cost stop option if you want to stay in Iceland for a bit.
From a strictly aviation standpoint, Iceland does provide a diversion airport on the trans Atlantic route but all things considered long distance flight is not the dangerous or difficult task as it once was.

Unfortunately I don't find a link for that right now, but the airport operator in KEF, Isavia, also decided to have unusually low landing costs to make flights more attractive and instead they try to get the money they need to run the airport from parking costs, which are up to 190 USD for a bus to stop once. That gives airlines using KEF as a hub an advantage to ones with other airports as a hub.

That might explain why last month Kansas City Int’l just started its first ever transcontinental flight last month: MCI-KEF. For some reason it was big news.

long distance flight is not the dangerous or difficult task as it once was. But it does require ETOPS certification. Flying via KEF offers a non-ETOPS option.

It lets an airline offer transatlantic service using aircraft that can't make the non stop trip, and/or don't meet the navigation requirements to fly the North Atlantic Track system.